The present invention relates generally to the treating of travelling webs, and more particularly to the treating of webs which are relatively inelastic, for instance carpets or rugs whose reverse side is coated with rubber or the like.
There are many instances where webs, such as rugs, carpets or the like, must undergo treatment in an apparatus. This is true for instance when the web is to printed, if it is to be dyed, if it is to be cut or otherwise processed. In such instances it is necessary not only to maintain the web under requisite tension as it undergoes the treatment, but also to control its appropriate positioning in the machine, that is to control the location of its edges with respect to the apparatus through which it travels. This is required in order to compensate for tension variations, to avoid uneven pulling on the web that could cause it become distorted, to prevent uneven winding-up of the web, and for similar reasons. From the prior art it is known to provide devices using regulating rollers which so control the position of the web transeversely to its direction of advancement that the edges--and thereby the longitudinal centerline of the web--are maintained in a certain relationship in the apparatus.
It is also known to utilize a different approach, avoiding the guidance rollers which extend over the entire width of the web and replacing them with edge guides which serve to urge the edges of the web to the desired position.
The trouble with both of these prior-art constructions is that there is a danger that folds may fold in the web, due to the lateral shifts caused in the web by the control elements. This is particularly true if the web is relatively inelastic, such as is for instance the case with rugs or carpets having a coating on the reverse side, usually latex or foam rubber.